Some computer systems, such as diskless desktop personal computers utilize storage devices remote from them. The computers utilize a network to access a disk drive device or storage system as though the disk drive was local to the computer. Some computer systems use dedicated network connections to perform network reads/writes with acceptable performance. SCSI (small computer system interface) commands are sent over the network to the remote storage. This is sometimes referred to as internet SCSI or iSCSI. A dedicated network for iSCSI storage is independent of the data network and uses two ethernet ports on the desktop and duplication of network routers.
When an end user or application sends a request, the operating system generates the appropriate SCSI commands and data requests, which then go through encapsulation and, if necessary, encryption procedures. A packet header is added before the resulting IP packets are transmitted over an Ethernet connection. When a packet is received, it is decrypted (if it was encrypted before transmission), and disassembled, separating the SCSI commands and request. The SCSI commands are sent on to the SCSI controller, and from there to the SCSI storage device. Because iSCSI is bi-directional, the protocol can also be used to return data in response to the original request.
iSCSI is one of two main approaches to storage data transmission over IP networks. An alternative method is called Fibre Channel over IP (FCIP), which translates Fibre Channel control codes and data into IP packets for transmission between geographically distant Fibre Channel SANs. FCIP (also known as Fibre Channel tunneling or storage tunneling) can only be used in conjunction with Fibre Channel technology; in comparison, iSCSI can run over existing Ethernet networks.